1. Field of the Invention
The present invention relates to a semiconductor wafer back-surface grinding method and a semiconductor wafer grinding apparatus for grinding the back surface of a semiconductor wafer, having a support base material adhered to a front surface with a circuit pattern formed thereon, for the purpose of reducing the thickness of the semiconductor wafer.
2. Description of the Related Art
In general, as processing methods for reducing the thickness of a semiconductor wafer, there is a method of grinding a back surface of the semiconductor wafer. For example, this method uses a grinding apparatus having a contact type sensor as an in-process gauge and, while the thickness of the semiconductor wafer is constantly monitored, grinding is performed until the wafer reaches a predetermined thickness that has been set in advance.
In this method, as shown in FIG. 3, the distance from the top surface of a turntable 2 to the back surface 3b of the wafer 3 is defined as the equivalent thickness (P1-P2) of the semiconductor wafer, and processing and measurement on the wafer can be performed simultaneously and in-process until the equivalent thickness (P1-P2) reaches δ1 without removing the semiconductor wafer 3 from the turntable 2, and the handling performance and the accuracy of the processing can be thereby improved.
However, in recent years, as increasingly large diameter and thin semiconductor wafers are required, due to the development of IC cards and 3-dimensional mounting, the above-described grinding method has a limitation in meeting these requirements. That is, in the above-described method of grinding the back surface 3b of a semiconductor wafer 3 using an in-process gauge, the semiconductor wafer 3 is directly fixed to the turntable 2, so that, when the wafer is machined until the wafer thickness δ1 is small, for example, as small as 30 μm, wafer strength is lowered and the wafer 3 is readily affected by a processing strain and this gives rise to cracking and warping.
As a solution to the above-described problem, there is a method, of grinding a back surface 3b of a wafer, shown in FIG. 4. In this method, a support base material 4 such as glass is adhered to front surface 3a of the semiconductor wafer 3, and the semiconductor wafer 3 is fixed to a turntable 2 via this support base material 4.
An example of a grinding method using an in-process gauge is disclosed in Japanese Unexamined Patent Publication No. 52-26686 (JP-A-52-26686), although it is not for grinding a semiconductor wafer, in which processing is performed while simultaneously measuring the inner diameter of a work piece with a gauge and, in accordance with the variation of size of the finished piece, a correcting command is given to the in-process control system.
When a support base material 4 is adhered to the front surface 3a of a semiconductor wafer 3, as shown in FIG. 4, the distance measured by an in-process gauge, that is, the distance (P1-P2) from the top surface of the turntable 2 to the back-surface 3b of the wafer, is the total thickness including the thickness t3 of the support base material 4 in addition to the thickness t2 of the protective surface film 5. As the tolerances (errors) of the protective film 5 and the support base material 4 are added, the single semiconductor wafer 3 cannot be finished to an accurate thickness. When a large number of semiconductor wafers 3 are continuously processed in batch processing, there is a problem that variation of the thickness of individual support base material 4 entails variation of the thickness of individual semiconductor wafers 3.